The present invention relates to the speed control of passenger vehicles, such as mass transit vehicles or the like, and including the decoding of wayside-provided speed codes for which vehicle speed control and speed maintenance purposes while the vehicle is moving along a roadway track.
It is known in the prior art to provide a checked redundancy speed error determination as disclosed in U.S. Pat. No. 3,749,994 of T. C. Matty. It is also known in the prior art to individually decode the ones data and the zeros data of an input speed command from the roadway track, and then to compare the ones data with the zeros data to detect any discrepancy as disclosed in U.S. Pat. No. 4,015,082 of T. C. Matty et al.
Mechanical and crystal filters have been used in past passenger vehicle speed control apparatus to receive the speed codes transmitted from the wayside to the vehicle via the running rails. The signal modulating scheme consists of a pair of discrete frequencies in the five to ten kilohertz range modulated by frequency-shift-keying and phase-shift-keying into a six-bit comma-free code.
Typically, four pairs of different frequencies are used to accommodate different blocks of tracks. A block is a section of track with individual detection and speed code transmission capability associated with it. The reception of these speed codes requires filters with narrow bandwidths, sharp cutoffs, and high stability. Mechanical and crystal filters have these characteristics and are intrinsically failsafe since they possess no failure mode which of itself would cause the overall gain or bandwidth to increase.
When coupled with a failsafe threshold detection circuit, mechanical and crystal filters provide a vital signal reception scheme with acceptable performance. They have been used in train control systems on board steel wheel and rubber tire vehicles in many mass transit systems.
A general description of the microprocessors and the related peripheral devices as shown in FIG. 4 of the drawings is provided in the Intel Component Data Catalog currently available from Intel Corporation, Santa Clara, Calif., 95051.